Size-dependent ignition temperature of metallic compounds fabricated by self-propagating high-temperature synthesis

Considering the diffusion reaction at solid interfaces, the ignition temperature of compounds fabricated by self-propagating high-temperature synthesis (SHS) is modelled with the help of size-dependent activation energy. As reactant size decreases, ignition temperature also decreases. This is because of increased contact areas between the reactants and the lowered diffusion barrier, both of which must be calculated specifically for reactants in nanoscale. The model predictions and experimental results are consistent for some metallic compounds.     

High strain rate sensitivity of hardness in quinary Ti-Zr-Hf-Cu-Ni high entropy metallic glass thin films

Quinary Ti-Zr-Hf-Cu-Ni high-entropy metallic glass thin films were produced by magnetron sputter deposition. Nanoindentation tests indicate that the deposited film exhibits a relatively large hardness of 10.4±0.6 GPa and a high elastic modulus of 131±11 GPa under the strain rate of 0.5 s⁻¹. Specifically, the strain rate sensitivity of hardness measured for the thin film is 0.05, the highest value reported for metallic glasses so far. Such high strain rate sensitivity of hardness is likely due to the high-entropy effect which stabilizes the amorphous structure with enhanced homogeneity.     

Correlation between supercooled liquid region and crystallization behavior with alloy composition of La-Al-Cu metallic glasses

Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La 86 x Al 14 Cu x (x=16 at%-20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled...     

一种高品质中空金属光波导

讨论了高品质中空金属光波导的工作原理及其制作工艺，制备了以金和银作为波导材料的中空波导管，并对空芯以及充入不同透明液体的液芯波导的透光特性进行了测试，结果表明：与中空介质波导相比，中空金属波导具有光传输损耗低，透过率对波导弯曲与失调不甚敏感等优点；而液芯金属波导的透光效率与透明材料的折射系数无关。文中描述了在特定波段内“中空光纤”的原理，并报道了Ｈｅ－Ｎｅ和ＣＯ２激光在中空金壁波导传输的实验结果。     

On the probability distributions of relaxation times in glasses

The scale of relaxation times in glasses has led to generalizations of the Drude model of the dielectric function in terms of an integral, containing a Drude kernel and a probability distribution. This integral equation is solved by a Mellin or a Stieltjes transform. Beyond known results, we obtain the probability distribution of the Havriliak-Negami dielectric function. Even more general classes of dielectric models can be dealt with, using Mellin's transform. They may serve as checks for numerical procedures applied to the underlying ill-posed problem, if experimental data for the dielectric function are used. Received: 2 February 1998 / Accepted: 17 March 1998     

Structural and magnetic properties of FIB-irradiated microstructures on a Pt/Co multilayer

We present a study of the structural and magnetic effects induced by focused 30 keV Ga⁺ ion beam irradiation on a Pt(2.8 nm)/[Pt(0.6 nm)/Co(0.3 nm)]₆/Pt(6.5 nm) ferromagnetic multilayer, using transmission electron microscopy, optical and magneto-optical microscopy. The work is of relevance to high-density data-storage applications, where media planarity is crucial for device reliability.     

永磁体等效磁矩的测量

在磁技术应用中，对永磁材料的主要磁性参数的研究及测量已成为人们关注的问题之一．本文提出通过测量磁场从而确定永磁体磁矩的一种简便方法，并就测量所涉及的有关问题作了讨论．     

Simulation of the interaction of light with 3-D metallic nanostructures using a proper orthogonal decomposition-Galerkin reduced-order discontinuous Galerkin time-domain method

In this artice, we report on a reduced-order model (ROM) based on the proper orthogonal decomposition (POD) technique for the system of 3-D time-domain Maxwell's equations coupled to a Drude dispersion model, which is employed to describe the interaction of light with nanometer scale metallic structures. By using the singular value decomposition (SVD) method, the POD basis vectors are extracted offline from the snapshots produced by a high order discontinuous Galerkin time-domain (DGTD) solver. With a Galerkin projection and a second order leap-frog (LF₂) time discretization, a discrete ROM is constructed. The stability condition of the ROM is then analyzed. In particular, when the boundary is a perfect electric conductor condition, the global energy of the ROM is bounded, which is consistent with the characteristics of global energy in the DGTD method. It is shown that the ROM based on Galerkin projection can maintain the stability characteristics of the original high dimensional model. Numerical experiments are presented to verify the accuracy, demonstrate the capabilities of the POD-based ROM and assess its efficiency for 3-D nanophotonic problems.     

Dynamics of hybrid shafts

In this paper the dynamic performance and cross-section deformation of shafts made of metals (steel and aluminum), composites (CFRP and GFRP) and hybrids of metals and composites have been studied. A layered finite degenerated shell element with transverse shear deformation and dynamic behavior is employed. Results obtained show that improvements in dynamic performance and reduction of cross-section deformation of hybrid shafts over metallic and composite shafts are possible.     

Synthesis and crystal structures of Ag and Hg complexes of bis(N-heterocyclic carbenes) on p-tert-butylcalix[4]arene platform

A series of p-tert-butylcalix[4]arene 1,3-diimidazolium salts were successfully prepared by the alkylation of p-tert-butylcalix[4]arene with dibromoalkanes, and sequential substitution reaction with 1-alkylimidazole. Furthermore, coordination reactions of p-tert-butylcalix[4]arene 1,3-diimidazolium salts with silver oxide and mercury acetate gave novel Ag and Hg complexes of bis(N-heterocyclic carbenes) on p-tert-butylcalix[4]arene platform. The single-crystal structures of four p-tert-butylcalix[4]arene 1,3-diimidazolium salts and three metal complexes were successfully determined by X-ray diffraction. An Ag–Ag argentophilic interaction (Ag–Ag bond length is 3.1599(6) Å) is formed between the two Ag–NHC complexes and a dimetallic coordination mode exists in Hg–NHC complexes.